The improvement of TEM 00 -mode laser conditions is a key focus in solar laser research, especially for applications requiring low divergence and high power density. Using multiple active media to mitigate thermal load is a promising strategy to enhance beam quality, scalability, and stability of laser output power. However, to our knowledge, no experimental research has been conducted on the emission of multiple TEM 00 -mode solar laser beams. This paper reports, to the best of our knowledge, the first simultaneous emission of four TEM 00 -mode solar laser beams, utilizing a heliostat-parabolic mirror system of PROMES-CNRS, alongside a laser head composed of an aspheric lens, a conical pump cavity, and four Ce:Nd:YAG rods in an end-side pump configuration. A total TEM 00 -mode laser power of 6.05 W was achieved, corresponding to an 8.77W/m 2 collection efficiency and a 0.90% solar-to-laser power conversion efficiency; these efficiencies represent new benchmarks for solar laser systems that incorporate parabolic mirrors, exceeding the previous records, set at the same facility by factors of 1.87 and 1.43, respectively.

A Monte Carlo simulation code was used to predict the solar-to-laser conversion efficiency of a fully planar solar-pumped laser. The calculations, which simulated an experimental setup with a diameter of 30 cm, reproduced the experimental results with a high degree of accuracy. The current experimental configuration yielded a limited laser power of 34 mW and a slope efficiency of 0.1%, which were attributed to incomplete spectral utilization and reflection losses of the photon confinement mechanism. In this study, the impact of each factor on efficiency degradation was quantitatively demonstrated, and avenues for future improvement were identified. The findings reveal that the solar-to-laser conversion efficiency can reach 17.4% under optimal conditions, namely, the utilization of quantum dots that fluoresce at near-infrared wavelengths and ideal mirrors exhibiting perfect reflectivity over the full range of incident angles and wavelengths.

Cr content χ of 0.4 at% for a Cr doped Nd (1 at%): YAG laser rod (LR) gave a higher laser output (Ioutput) than that of 0.0, 0.7, and 1.0 at% in a specially designed compact solar-pumped laser (SPL) outdoors. Ioutputs were measured as a function of an 808 nm pumping laser’s power indoors, changing the transmittance of the output coupler. From the obtained slope efficiencies, round-trip resonator losses Ls for the four χs were estimated, and the best-fit function L(χ) was derived. From the experimentally estimated Cr-to-Nd effective energy transfer efficiency ηCr→Nd at the four χs, the best-fit function ηCr→Nd(χ) was derived. Using L(χ), ηCr→Nd(χ), and a wavelength λ- and χ-dependent absorption coefficient α(λ, χ), inferred from the literature, the power conversion efficiency ηpower(χ) under 1 Sun was estimated. The estimated ηpower(0.4) and ηpower(0.7) were reproduced in experimentally deduced factors at the mode-matching efficiency ηmode = 0.19. The estimated maximum ηpower(χ) appeared around χ = 0.2 at%, being 20% higher than that at χ = 0.4 at%. In addition to this, a composite LR (Cr, Nd: YAG core/Gd: YAG cladding) was found to achieve ηmode = 0.68 and ηpower = 0.064, ranking among the highest-class SPL ηpowers.

A high-power and highly efficient solar-pumped laser has been reported. A Fresnel lens with an effective area of 2.73 m2 was utilized to collect solar radiation for the side-end mixed pumping of a Ce:Nd:YAG crystal rod with a diameter of 7 mm and a length of 90 mm. Under a solar irradiance of 825 W/m2, the system achieved a continuous laser output of 89.29 W at a wavelength of 1064 nm, resulting in a solar-to-laser conversion efficiency of 3.96% and a collection efficiency of 32.71 W/m2. The output power of 89.29 W represents 1.54 times the highest previously reported value for the Ce:Nd:YAG crystal utilized in solar laser generation, and the conversion efficiency is 1.51 times greater than that of corresponding studies. Furthermore, the conversion efficiency of 3.96% surpasses the existing record for the combination of Fresnel lens and single rod configurations by a factor of 1.02, while the laser output is 3.32 times greater than that of related research.

The urgency of climate change mitigation has driven scientific research and technological advancements in the pursuit of sustainable energy solutions, positioning solar energy as one of the most promising renewable resources to help reduce dependence on fossil fuels. Solar-pumped lasers are specifically designed to directly harness and convert a portion of the Sun’s incoherent radiation into coherent laser light, paving the way for the advancement of environmentally friendly laser technology. Nearly two decades ago, our research team at the NOVA University of Lisbon embarked on this topic with the goal of significantly enhancing the performance of solar-pumped lasers, whose endeavors positioned us at the forefront of this field. This article highlights the latest advancements of this renewable technology accomplished by our research team through pioneering experiments with Ce:Nd:YAG as a novel active medium for solar lasers and the exploration of innovative schemes for simultaneous pumping of multiple media. Notable progress included the establishment of new records in solar laser efficiency for both multimode and fundamental mode regimes and attaining the lowest threshold pump power for solar laser emission. Significant improvements were also achieved in thermal management and solar tracking error compensation capacity, which have resulted in enhanced laser output power stability. These developments are critical for the practical application of solar-pumped lasers.

One of the major goals of solar-pumped lasers is to improve T E M 00-mode collection and conversion efficiencies. Several studies have explored multi-rod designs with the aim of enhancing laser output and thermal management by distributing the absorbed solar energy across multiple rods. In this work, we introduced a concept comprising four Fresnel lenses with a total collection area of 3.14m 2 and four aspherical lenses, which concentrated the sunlight into a water-flooded cylindrical cavity housing five side-pumped Ce:Nd:YAG rods. A beam-merging scheme was also proposed to generate a single output beam. Simulations performed with Zemax and LASCAD demonstrated that this configuration could produce a total T E M 00-mode laser output of 162.3W. The corresponding collection efficiency reached 51.7W/m 2, with a solar-to-laser power conversion efficiency of 5.44%, representing improvements of 3.13 and 2.64 times, respectively, compared to the record experimental results from a system using a single Ce:Nd:YAG crystal and a Fresnel lens. Moreover, even when compared to a more complex seven-rod configuration, both efficiencies exhibited a 1.50 times increase.

Optimization of parameters for solar-pumped laser using Fresnel lens

A multirod Ce:Nd:YAG solar laser approach, using a Fresnel lens as a primary concentrator, is here proposed with the aim of considerably increasing the efficiency of solar-pumped lasers. Fresnel lenses are cost-effective, rendering solar lasers more economically competitive. In this work, solar-pumped radiation collected and concentrated using the Fresnel lens is received by a secondary three-dimensional compound parabolic concentrator which transmits and funnels the light toward the Ce:Nd:YAG laser rods within a water-cooled tertiary conical concentrator that enables efficient multipass pumping of the rods. To explore the full potential of the proposed approach, the performance of various multirod configurations is numerically evaluated. Through this study, configurations with three and seven Ce:Nd:YAG rods are identified as being the most efficient. A maximum continuous wave total laser power of 122.8 W is reached with the three-rod configuration, marking the highest value from a Ce:Nd:YAG solar laser, leading to solar-to-laser conversion and collection efficiencies of 7.31% and 69.50 W/m2, respectively. These results represent enhancements of 1.88 times and 1.79 times, respectively, over the previous experimental records from a Ce:Nd:YAG/YAG single-rod solar laser with a Fresnel lens. Furthermore, the above results are also 1.58 times and 1.68 times, respectively, greater than those associated with the most effective three-rod Ce:Nd:YAG solar laser utilizing a parabolic mirror as the main concentrator. The present study also shows the great usefulness of the simultaneous pumping of multiple laser rods in terms of reducing the thermal stress effects in active media, being the seven-rod configuration the one that offered the best compromise between maximum efficiency and thermal performance. This is crucial for the applicability of this sustainable technology, especially if we wish to scale our system to higher power laser levels.

The Nd:YAG, Ce:Nd:YAG, and Cr:Nd:YAG active media in multi rod configuration are investigated for solar-pumped lasers using simulation methods. A statistical model employing Monte Carlo photon tracing simulates a laser system with multiple rods for combined end-side solar radiation pumping. The model enables one to evaluate efficiency, pump distribution, and output parameters of solar lasers. Simulation analyses is conducted on a three-rod setup using the aforementioned active media. Comparative results demonstrate that Cr:Nd:YAG achieves the highest efficiency, reaching an overall conversion efficiency of 5% at 500 W pump power, which is twice that of Nd:YAG lasers under similar conditions.

A slope efficiency of 0.1% has been achieved for a fully planar solar-pumped fiber laser (SPFL) with a diameter of 30 cm and an output power of 34 mW. The fiber length is constrained to 400 m, but numerical simulations indicate that the maximum laser output power can be elevated to 113 mW by simply extending the length of the fiber and housing it in the same body. The tolerance to the solar tracking error was quantified, and the results demonstrated that more than 80% of the maximum output power can be sustained up to a ±23° tracking error. This study demonstrates the capability of the fully planar SPFL to operate without solar tracking.

Luminescent properties were characterized and investigated in Ca2KMg2V3O[Formula: see text] phosphor. Near infrared (NIR) emission of Nd[Formula: see text] activator in Ca2KMg2V3O[Formula: see text] host is reported for the first time. NIR emissions around 1[Formula: see text][Formula: see text]m due to characteristic lanthanide transitions are observed. Excitation spectra reveal that the NIR emission is host-sensitized. The sample was prepared by solution combustion synthesis method. Ca2KMg2V3O[Formula: see text] is a self-activated phosphor belonging to cubic system having space group [Formula: see text] with z = 8, a = 12.5 Å. Strong host emission was observed in the blue–green region. It displays broadband emission with an intense band centered at 508[Formula: see text]nm that spans almost the whole visible light spectrum, from 400[Formula: see text]nm to 700[Formula: see text]nm due to the d–d transition of V[Formula: see text] ions in the (VO[Formula: see text] groups. The Ca2KMg2V3O[Formula: see text]:Nd[Formula: see text] phosphor showed NIR emission at 1072[Formula: see text]nm due to transition 4F[Formula: see text]I[Formula: see text], for 343[Formula: see text]nm excitation. Obtained results indicate the significant potential of Ca2KMg2V3O[Formula: see text] phosphor for solid state laser applications. The strong absorption resulting from f–f transitions in the 470–890[Formula: see text]nm range makes the phosphor appropriate for a number of applications, including solar-pumped lasers.

Developing a high quality ceramic laser gain medium for solar directly pumped solid state lasers is essential, and yet the light conversion efficiency of the gain media for solar pumping remains a challenge. In this study, Ce and Nd ions, co-doped YAG transparent ceramics with theoretical transmittance and stable Ce3+ valent state were developed, and revealed that the absorbed visible light and light conversion efficiency in Ce,Nd:YAG ceramics were 3.98 times and 1.34 times higher than those in widely reported Cr,Nd:YAG ceramics, respectively. A concentration matching principle between Ce3+ and Nd3+ ions in YAG was established, and a higher Nd3+ ion doping concentration with a relatively low Ce3+ concentration was favorable to improve both the light conversion efficiency and emission intensity at 1064 nm of Ce,Nd:YAG ceramics. Energy transfer efficiency from Ce3+ to Nd3+ of the 0.3 at.%Ce,1.5at.%Nd:YAG ceramic reached as high as 61.71% at room temperature. Surprisingly, it was further promoted to 64.31% at a higher temperature of 473 K. More excited electrons at the upper energy level of Ce3+ ion under the high temperature accounted for this novel phenomenon. This study proposes a new design strategy of gain materials for solar directly pumped solid state lasers.

In this paper, we investigate the role of solar laser technology as a pivotal element in advancing sustainable and renewable energy. We begin by examining its wide-ranging applications across diverse fields, including remote communication, energy storage through magnesium production, and space exploration and communication. We address the current challenges faced by solar laser technology, which include the necessity for miniaturization, operation at natural sunlight intensity without the need for concentrated power, and efficient energy conversion. These improvements are essential to elevate their operational performance, beam quality, and cost-effectiveness. The promising prospects of space-based solar-pumped lasers and their potential role in magnesium generation for a sustainable energy future highlight some of the vast application opportunities that this novel technology could offer.

We studied transversely solar-pumped Nd3+ doped fiber laser with parabolic trough via simulation models developed by Monte Carlo photon tracing method. Our analysis involved estimating losses at cavity walls and the absorption efficiency within the fiber core. Factoring in the absorption distribution of pumped solar radiation in the fiber, we determined an absorption efficiency of 8% for a 287 meter long fiber arranged in a semicircular configuration. Subsequently, our calculations found a laser output of 3.03 W for this fiber laser system, resulting in an overall conversion efficiency of 4.29% from solar to laser beam.

A solar-pumped laser with bulk active medium generally requires a considerable amount of concentrated solar power for initiating laser emission. In previous work, 54.9 W threshold incoming solar power was found for a Ce:Nd:YAG solar laser by a 0.075 m2 effective area parabolic mirror. In the present work, a 0.0615 m2 area Fresnel lens was used to concentrate incoming solar power to a 2 mm diameter, 30 mm length Ce:Nd:YAG rod. 1.81 W continuous-wave 1064 nm solar laser output power was measured, corresponding to 3.15% solar-to-laser conversion efficiency, 4.4% laser slope efficiency, and 29.4 W/m2 collection efficiency. More importantly, threshold incoming solar power as low as 16.5 W was achieved, representing a 3.33 times reduction in threshold solar power, as compared to previous record by the parabolic mirror. By using a 0.0855 m2 area Fresnel lens, 2.83 W solar laser power was also measured, leading to 3.56% solar-to-laser conversion efficiency, 4.9% laser slope efficiency, and 33.1 W/m2 collection efficiency. Low threshold incoming solar power of 22.7W was also obtained, representing a 2.42 times reduction in threshold solar power in relation to the previous record. Notably, 1.41 W TEM00 mode solar laser power was also measured by adopting an asymmetric laser resonant cavity, resulting in 2.06% solar-to-TEM00 mode laser conversion efficiency, which, to the best of our knowledge, is 2.61 times larger than the previous record by Nd:YAG medium.

A high-power solar side-pumped Nd-doped fiber laser based on a doughnut-shaped hollow reflector (DHR) is proposed. The primary concentrator consists of twelve off-axis parabolic mirrors. The DHR coupled with an array of three-dimensional compound parabolic concentrators (3D-CPCs) functions as the secondary concentrator, inside which many cycles of Nd-doped fiber is coiled. After being reflected by the off-axis parabolic mirrors, the sunlight is launched into the DHR through the twelve 3D-CPCs, and experiences multiple-times reflection by the DHR, and finally is absorbed by the Nd-doped fiber for laser oscillation. Ray tracing shows that 173-W of solar power can be absorbed by the fiber. By solving the rate equations and power transmission equations, laser output power, slope efficiency and optical-to-optical conversion efficiency of 10.3 W, 6.12% and 5.94%, respectively, are realized. This kind of solar-pumped fiber laser thus offers a new route for achieving high-power solar-pumped laser sources.

Investigation of a 100 W Solar-Pumped Disk Laser with TEM00 Output

Laser beams with a doughnut-shaped profile have garnered much attention for their contribution to trapping nanoparticles and improving the scanning speed during laser-based 3D metal printing. For this reason, the production of a doughnut-shaped solar laser beam by end-side pumping a Ce:Nd:YAG rod with a small reflective parabolic collector was investigated. The resultant beam profile shape depended on the absorbed solar power, displaying a TEM00-mode profile at elevated input power. This phenomenon was primarily attributed to the role of distributing energy around the central region of the crystal. In contrast, at lower input power, a doughnut-shaped beam emerged, characterized by minimal energy distribution at the center. Through experiments conducted with a collection area of 0.226 m2 and a nominal solar irradiance from 970 W/m2 to 1000 W/m2, it was demonstrated that sufficient energy was available to generate a doughnut-shaped beam with a solar laser collection efficiency of 5.96 W/m2, surpassing previous measurements by 1.32 times. Further research with a larger collection area of 0.332 m2 and a diverse solar irradiance range of 650 W/m2 to 800 W/m2 revealed that the presence of a thin layer of cloud caused a transition from a doughnut-shaped to a TEM10-mode and, eventually, a TEM00-mode as the absorbed input solar power increased. Notably, under heavier cloud cover, the laser beam exhibited deformation at low input power instead of maintaining a doughnut-shaped profile. This research significantly enhances our comprehension of doughnut-shaped solar laser beams and their reliance on solar energy. By harnessing the plentiful and readily accessible energy from the Sun, the incorporation of solar energy into the realm of solar-pumped lasers holds immense promise for promoting sustainability. This transformative utilization can progressively diminish the industry’s carbon footprint, yielding long-term environmental benefits.

For decarbonization of ammonia production in industry, alternative methods by exploiting renewable energy sources have recently been explored. Nonetheless, they still lack yield and efficiency to be industrially relevant. Here, we demonstrate an advanced approach of nitrogen fixation to synthesize ammonia at ambient conditions via laser–induced multiphoton dissociation of lithium oxide. Lithium oxide is dissociated under non–equilibrium multiphoton absorption and high temperatures under focused infrared light, and the generated zero–valent metal spontaneously fixes nitrogen and forms a lithium nitride, which upon subsequent hydrolysis generates ammonia. The highest ammonia yield rate of 30.9 micromoles per second per square centimeter is achieved at 25 °C and 1.0 bar nitrogen. This is two orders of magnitude higher than state–of–the–art ammonia synthesis at ambient conditions. The focused infrared light here is produced by a commercial simple CO2 laser, serving as a demonstration of potentially solar pumped lasers for nitrogen fixation and other high excitation chemistry. We anticipate such laser-involved technology will bring unprecedented opportunities to realize not only local ammonia production but also other new chemistries .

We have developed a fully planar solar-pumped fiber laser using a solid-state luminescent solar collector (LSC). This laser does not use any focusing device, such as a lens or mirror; thus, it can lase without tracking the sun. Our developed device with an aperture of 30 cm emits 15 mW, corresponding to an optical-to-optical conversion efficiency of 0.023% and a collection efficiency of 0.21 W/m2. A 12-fold improvement over a previously developed liquid LSC is achieved by combining the total internal reflection of the solid-state LSC with dielectric multilayer mirrors. The observed laser power is in good agreement with that predicted via numerical simulation, demonstrating the effectiveness of our proposed method.